Hey! 350 TBI motor chugging somtimes Please help pulling hair out

Hey everyone. Ive been having this issue with my 350 TBI motor in my 87. Sometimes not all the time it will like chug and kind of spit and sputter and have no power when i hit the gas. And most the time it is gutless untill i throw my foot into it then it gets to high R's and goes like a bat outta hell. I have replace fuel filter rebuilt Throttle body new fuel injectors have a new fuel pump that i havint put in yet set my timing. so i am lost and have no idea what is causing this. I have unplugged my egr to see if that was causing it and nope. to my knowledge there is no vaccume leaks. Pleas give me advice where to go from here. I was thinking next it is new coil and ignition mod but i am really sick of throwing parts at it and it not being the problem. Any input is appreciated, as i am LOST!! Ha thank you:happy:

You'll have to take a spray bottle with water in it, and check all the engine mating surfaces for leaks. Are you getting any codes from the ecm? Check ALL connections, clean the ground wire contact points. Does the timing stay stable on the mark, or does it wander at all? You should be able to watch the TBI work as you check for part throttle response. Does it sputter, or is it smooth? If it sputters, you may need that new pump. If the spray stays good, and the engine stumbles, it could be the ignition system. Can you give the engine a compression test? Pull all the plugs, as well as the Batt wire off the dist. Check for compression one at a time, cold. Post the numbers as well as how the meter reacts. Does it build up over three or more strokes? You didn't mention cleaning the air filter, or the PCV valve and filter. Your motor may have a bad crank sensor, or throttle position sensor. Could even be a bad batch of gas, just relax, and keep fighting. You'll win out if you don't give in. Check your tank cap, remove it, and run the truck, and see if it helped. A nonvented or plugged cap will make it hard for the pump to draw fuel from the tank. My truck worked but the fuel tank made a lot of noise, until I solved that one. Pulling the cap off at the filling station, and hearing air whoosh into the tank, was a dead give away. Good luck.
Brian L.

RallySTX makes some good points but we are at a dissadvantage not knowing exactly what we're dealing with. Is this a station wagon a boat or a truck? I'm guessing truck but you get my point. Knowing what year, make, model, transmission, any after maket accessories, how many miles etc. will help to figure out what may be going on.
From your description I would think you are getttin enough fuel if it runs well at Wide Open Throttle. Maybe a throttle position sensor not reading right at low to part throttle.

Hey thanks for the help i will start digging into them things and hope for something. Dpeter it is a 1987 silverado V-10 with dana 44 axles under it. It has a R400 tranny i believe. I tested my throttle positon sensor with a gauge and it seemed to send good signal all the way through the throttle. No i am not getting any codes although sometimes my checkengine light pops on while driving but then it will go out I unplugged my o2 sensor then i got the check engine light so i know thats working. It is odd to because today it chugged around a little big then it started running good like it had no problems and there was less fuel in the tank and it is normally oposite if i run it below a 1/4 tank I think it runs like crap but not today i dont know and there has been a couple tanks through this thing so i know its not bad gas. It will run fine and have great throttle response and the spray is perfect when its sitting in my garage but when i get it on the road that is when i get the sputter and I cant be under the hood then. I farm here in wisconsin and i can pull pretty heavy **** with my truck and it has no problem with that power so im not sure compression is a problem tho it could be. another thing youall should know is it takes a while to start up and i was thinking this could be a hint! not sure what kind of a hint but its somthing haha. When i timed it i got it to 0 and it stayed there and then shut it off and plugged in the electronic timing wire back in so i figured that automatically changes it? I will do a compression test this weekend and post the results and I didint know there was a battery wire on the distributor? Brand new air filter and im not sure where abouts the pcv valve is or its filter is? And crank sensor that can affect startingtoo cant it? This is my first 350 so im kind of a dummy when it comes to them right now. Thanks for all your help! I can post pictures of motor or anyting if yall would like and how can i check the vacuum lines for leaks with a water bottle? all i did was make sure they are all plugged in and made sure they dont sound like they are leaking... Thanks!

I had a similar problem with an 87 Cavalier, hard to start, idled ok but under light load and steady state cruising it would miss and buck but stick your foot in it and all was good. Turned out to be an EGR valve stuck open and passing enough exhaust to realy screw it up. I too went through what you are until someone enlightened me. Try cleaning it, buy a new one or do what I did and make a blank off plate and plugged the exhaust tube. Can't remember if I just crimped the tube or plugged the manifold.

Update: I think I found the problem tonight but I need direction on how to fix it and I will explain the best I can. So vaccume line right behind the throttle body that is in front of distributor seemed to be cracked around the end so I seen it when it was idol in my garage. Anyway i unplugged it and it made my truck idol way faster, cut off the crappy end and stuck it back on and then i heard the leak which i thought it was from my manifold but turns out its the vaccume line that runs right next to the manifold and accually goes into the front of the manifold to i think the back of the block?? not sure tho didint get a good look at it. then i started really looking at them back vaccumes and I think a valve or somthing is stuck because that line i fixed it is sucking so hard its squeezing the hose together. so what im looking to do is block off these emisions and vaccume lines as much as possiable i just need to know what hoses are needed to run good and which hoses i should block off so i get my truck back running how it was. Thank you guys in advance. lets see if this is the problem!

A vacume line pulling enough pressure to colapse the line, is getting manifold vacume. The 87 Chevy trucks had several vacume operated systems. ANY vacume leak will likely cause rough running issues. There should be a VECI label on the inner fender skirt, the radiator shroud,, or the air cleaner housing. Simply make sure that any vacume lines you see are routed correctly, and that there are no leaks. Trouble is, on older vehicles like that, those lines age and become soft or awolen, causing leaks that aren't easy to see. If you could get to Janesville, I could look it over, and help out. The EGR valve is a round metal cap type deal next to the TBI. It bolts to the intake and has a hose or two on top of it.Sometimes you can get your fingers up under the lip, and push upward on the inner diaphram and watch the engine react to it. If there is no reaction, it's likely plugged, and needs cleaning. Or it may be stuck, and passing exhaust as posted earlier. There are several sensors on the engine that have a direct effect on how it runs. A vac line that starts on the engine, and goes to the back area, likely goes to the firewall, and may be for the vent controls. Next time you run the truck, get it going, and see if you can switch from defrost to floor heat with the control slider on the dash. While the engine is still warming up, pop the hood, remove the flexible hose that goes from the air snorkel to the exhaust manifold, and stick your finger up into the hole. You want to see if the little flapper valve is open, allowing the engine to draw hot air from the exhaust manifold into the engine. If you can't find a VECI label for the truck, you may need to order one from the factory. It should be fairly cheap, or you could go to a couple salvage yards and find a truck with the same setup yours has, and simply copy or get good pix of it, and see if it matches.
Brian L.